# power rating of resistors?

Discussion in 'General Electronics Chat' started by stanman11, Mar 15, 2011.

1. ### stanman11 Thread Starter Member

Nov 23, 2010
230
4
im trying to figure out if the bigger the resistor the more power it lets through or the mor power it blockes?

2. ### Audioguru Expert

Dec 20, 2007
10,674
1,191
The physical size of a resistor determines how much heat it can transfer to air.
Its value (the number of ohms) and the voltage or current determines how much it "blocks" or passes current flow.

3. ### SgtWookie Expert

Jul 17, 2007
22,202
1,793
Ohm's Law will help you understand the relationships between resistance, current and voltage.
1 volt across 1 Ohm's resistance = 1 Ampere of current and 1 Watt of power.
I=E/R; P=EI
E=IR
R=E/I
Etc.
It's a good idea to double your power requirement when selecting a wattage rating; that ensures your resistors will be able to dissipate the power.

If you needed to use a 100 Ohm resistor with 10v across it, then the current would be 10/100 = 0.1A (100mA), and you would select a resistor that was rated for 10v*0.1A=1 Watt; double it for reliability = 2 Watts.